(9f) A Review of Coal Devolatilization with Very Slow Heating Rate

A review has been provided for coal devolatilization process with very slow heating rate less than 20K/min. The yield of volatiles of liquid and gaseous species is a function of operational conditions, including effects of reactor atmosphere gases, coal ranks, heating rates, ultimate devolatilization temperatures, pressure, soak time at ultimate temperatures, and catalysts. One important factor of coal devolatilization is the extent of secondary reactions. Various research groups obtained contradictory observations for the volatile yields, e.g., as a function of the heating rate. Of the most importance, higher volatile yields are obtained if the operational conditions allow secondary reactions to proceed so that coal can be degraded to tar, and tar to gaseous species. The other important factor is the reactor atmospheric gases. The two reacting gases are hydrogen and steam. Hydrogen atmosphere enhance the secondary reactions during the coal pyrolysis, and the effect of steam atmosphere is obtained because of physical processes that degrade and rupture fragments from coal and tar. Certain catalytic effects are found in various coal devolatilization experiments. Again, minerals in coal samples catalyze the devolatilization process by enhance the secondary reactions by weakening chemical interactions with forming interactions between the volatile matter and mineral particles.